Cornea is a transparent, non-vascular tissue having a diameter of about 1 cm and a thickness of about 1 mm. The transparency of cornea affects the visionary function. Various physiological and biochemical phenomena in cornea work functionally, mainly for the purpose of maintaining the transparency of cornea.
Corneal epithelial defects caused by various diseases such as corneal ulcer, corneal erosion, keratitis and dry eye is spontaneously repaired unless mixed infection is associated. When the repair is delayed or not completed or the epithelial defect is prolonged with some reason, however, not only the normal construction of corneal epithelium is badly affected but also even the constructions and functions of the corneal stroma and endothelium are damaged. The principle of the therapeutic methods according to the conventional art is passive. That is, the therapeutic methods include protecting the corneal surface from external stimulation to intend spontaneous extension of corneal epithelium for re-surfacing the defected area. Following the development of cell biology in recent years, factors involved in proliferation, migration, adhesion, extension and the like have been elucidated. It was reported that compounds promoting the extension of corneal epithelium play important roles in repairing corneal epithelial defects (Japanese Journal of Clinical Ophthalmology, 46, 738-743 (1992); Japanese Journal of Ophthalmologic Surgery, 5, 719-727 (1992)).
Meanwhile, insulin-like growth factor is one of growth factors regulating growth of normal human cells like epidermal growth factors, fibroblast growth factors, platelet-derived growth factors and transforming growth factors and includes insulin-like growth factor-I (referred to as “IGF-I” hereinafter) and insulin-like growth factor-II (referred to as “IGF-II” hereinafter). Recently, for example, it was reported that IGF-I stimulates the proliferation of thyroid cells (J. Biol. Chem., 264, 18485-18488 (1989)) and that IGF-II regulates the muscle growth and differentiation (Hum. Mol. Genet., 3, 1117-1121 (1994)). In the field of ophthalmology, it was disclosed that IGF-I, IGF-II and their functional derivatives promote the survival of retinal neurons (the publication of Japanese Patent Publication (Tokuhyo) 7-500839); that IGF-II is widely effective for the treatment of all types of wounds mainly including lesions made during keratoplasty (the publication of JP-A-63-233925); and that a solution containing the growth factors can be used to keep eye tissues such as cornea to be used for keratoplasty at their fresh state even in a circumstance at low a temperature (the publications of JP-A-5-25001 and JP-A-6-48901). Further, another disclosure is made about a gel composition containing a growth factor that the gel composition is generally effective for wound healing of for example the anterior segment of the eye (the publication of JP-A-2-112).
On the other hand, substance P is a polypeptide consisting of 11 amino acids and has actions such as vasodilatation, the smooth muscle contraction, the promotion of salivary gland secretion, and diuresis. In the field of ophthalmology, it is disclosed that substance P can improve abnormal secretion of the goblet cells of conjunctiva (the publication of International Publication WO95/13087), while the kinetics of substance P in the case of inflammation such as keratitis is also reported (Nippon Ganka Gakkai Zasshi, 91, 982-987 (1987); Nippon Ganka Gakkai Zasshi, 92, 448-452 (1988); and the like). As described above, various studies have been done. Additionally, the publication of JP-A-10-17489 describes that the tetrapeptide Phe-Gly-Leu-Met-NH2 (SEQ ID NO: 2) (referred to as “FGLM” hereinafter) on the C terminal of substance P when used in combination with IGF-I can promote wound healing of corneal epithelium and that the FGLM (SEQ ID NO: 2) is the minimum unit among partial peptides with such action of substance P. However, it has never been identified yet which amino acid sequence site in IGF-1 is responsible for the expression of the effect while IGF-1 is a polypeptide consisting of amino acids as many as 70.
Skin wounds are those of surface tissues, including a rupture, an abrasion, a surgical incision, a skin ulcer or a burn. Such skin wounds are treated by applying an emergency treatment to a wounded site and waiting for the wounds to spontaneously heal via the biological recovering power of their own. Such spontaneous healing requires a long time until recovery and pain continues during the term. Therefore, it is preferable that wound healing is actively promoted, by administering an agent for wound healing to wounded sites.
Because new epithelial tissues and connective tissues are formed through cell migration and growth in the course of wound healing, a pharmaceutical agent promoting or stimulating cell migration, differentiation and growth participating in wound healing is possibly an agent for wound healing. As such agent for wound healing, for example, lysozyme chloride and solcoseryl have been known.
However, the existent agents for wound healing do not have sufficient actions for promoting the wound healing so they are problematic in that they cannot completely heal wounds in a short period of time. It is considered that the cause is due to low contributions of these agents for wound healing to for example the re-surfacing of epidermis, collagen synthesis, the improvement of peripheral circulation, granulation, and angiogenesis, which are important elements in the course of wound healing.
There is no report about the minimum unit for exhibiting the activity in IGF-I and there is no report about the peptide per se of the amino acid sequence represented by Ser-Ser-Ser-Arg (SEQ ID NO: 1). Additionally, there is no report about the action of a joint administration of a peptide containing the amino acid sequence represented by Ser-Ser-Ser-Arg (SEQ ID NO: 1) and a peptide containing the amino acid sequence represented by Phe-Gly-Leu-Met-NH2 (SEQ ID NO: 2) for corneal disorders or the action thereof for skin diseases.
Generally, peptides consisting of numerous amino acids when administered into biological organisms are apt to be cut owing to metabolism and the like. Additionally at a stage of their formulation for use as pharmaceutical agents, the peptides are apt to be decomposed. It is desired that a peptide should have a chain as short as possible. Because the pharmacological activity thereof should be retained, however, it is an important subject in the development of pharmaceutical products to find the minimum unit for the exhibition of the activity of a long-chain peptide. IGF-I is a long-chain peptide consisting of amino acids as many as 70. It is a very important subject for the preparation of a more useful pharmaceutical product to find the minimum unit for the exhibition of the activity of IGF-I. Still additionally, it is a very interesting subject to make studies about specific pharmacological actions, namely the action on corneal disorders and the action on skin wounds, using the minimum unit for the exhibition of the activity.